Organic nitrogen compounds used to modify physical properties of thermoplastic polymers



Patented May 8, 1 951 ORGANIC NITROGEN COMPOUNDS USED TO MODIFY PHYSICAL PROPERTIES OF THERMOPLASTIC POLYMERS Edward L. Kropa, Old Greenwich, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application July 25, 1947, Serial No. 763,763

1 Claim. 1

This invention relates to thermoplastic polymeric materials and. more particularly, to a process for modifying the physical properties of thermoplastic polymeric materials.

Thermoplastic polymers and, in fact, almost any particular type of resin possess, for a given use or application, certain properties which are advantageous and certain other properties which are disadvantageous. Thus, a set of certain socalled advantageous properties might make a resin suitable for an application wherein the corresponding set of so-called disadvantageous properties is immaterial. On the other hand, however, in many cases the disadvantageous properties will interfere with the benefits desired from the advantageous properties.

To take a specific example, polystyrene may be considered. Polystyrene has good electrical properties and therefore should be extremely useful in the manufacture of molded articles for use in electrical equipment. Moreover, polystyrene is transparent, readily colored, relatively strong and easily molded and it should therefore find wide use in the manufacture of various novelties and household articles. However, polystyrene has relatively poor heat resistance and as a result of this property its application in the fields just mentioned has necessarily been somewhat limited. For example, in many electrical applications of molded plastics there is a possibility of exposure to relatively high temperatures as a result of heat generated in resistance coils and heat generated by electronic tubes, batteries, etc. Similarly, household articles of molded polystyrene are necessarily often exposed to temperatures at least as high as boiling water. Unfortunately, if articles molded of polystyrene are subjected to even moderately high temperatures they become distorted either because of internal strains if they have been injection molded or as a result of subjection to any load while at an elevated temperature.

As described in the copending application of Murray G. Sturrock, and Thomas Lawe, Serial No. 563,453, filed November 14, 1944, now abandoned, it has been found that polymers of dimethyl styrenes have improved heat resistance over that of polystyrene itself. They are therefore suitable for use in electrical equipment or in the manufacture of household articles for which polystyrene itself has not been entirely satisfactory.

According to the present invention I have discovered a process according to which styrene,

monoalkyl substituted styrenes and monohalogen substituted styrenes may be polymerized to produce a polymeric material of modified physical properties and particularly, a polymeric styrene of improved heat resistance comparable to the polymerized dimethyl styrenes.

Another specific example of thermoplastic polymeric materials to which the present inven tion may be applied consists of the polyacrylates, i. e., polymerized acrylic and alkacrylic acids, esters thereof, acrylonitrile, acrylamide, etc. Polyacrylates tend to be rubbery products and hence cannot be used satisfactorily in certain applications for which this property makes them unsuited. A polyacrylate of improved toughness and increased tensile strength may, however, be prepared according to my invention.

According to the present invention, therefore, I have discovered that when certain vinyl compounds are polymerized in accordance therewith the very nature of the polymer itself is changed and greatly increased molecular weights with consequent improved mechanical properties are obtained.

It is an object, therefore, of the present invention to provide a process for modifying the physical properties of thermoplastic polymers such as polystyrenes, polyacrylates, etc.

Another object of the present invention is to provide an improved process for the polymerization of monomeric compounds containing a single polymerizable CH2=C group to produce polymeric materials soluble in organic solvents.

A further object of the present invention is to brin about polymerization of a monomeric substance containing a single polymerizable The invention will be described in greater detail in conjunction with the following specific examples in which proportions are given in parts by Weight unless otherwise indicated.

3 EXAMPLE 1 75 parts of styrene (which has been steam-distilled from a 2% sodium hydroxide solution) 4, The results obtained, including those of Example 1 for the sake of completeness, are summarized in Table I.

Table I Catalyst Styrene Polyvinyl Alcohol Polymer Benzoyl Potassium Peroxide Persulfatc Compound .7 Paris if Type Parts Sty- Parts Sty- Parts Sty- Form Color Molding M. W.

rene rene rene 75 10 A-fiigfi 1.125 1.5 0.075 0.1 melamine-.. beads. good clear, good color" 81,000 75 10 Zio.' ..l 0.375 0.5 0.15 excellent.-- s1. haz good 00,200

co or. 75 10 do 0.75 1.0 0.15 good clear, good eolor. 69,000 75 10 do 1.125 1.5 0.15 ir sl.hazy,faircolor. 66,500 75 10 do 3.0 4.0 1.5 do do powder.

75 .do 1.125 1.5 0.02 0.027 .do powder good 101,000 75 10 Bagged. vis# 0.75 1.0 0.15 0.2 0.02 0.027 .-...do beads ex'cellehL. clear, excellent 80.000 C 01.

75 10 do 1.5 2.0 0.15 0.2 0.02 0027 do powder .do clear, goodcolorx. 68, 500 150 do 1.5 2.0 0.15 0.2 0.02 0.027 d0 o good clear, very good 79,000

75 10 A-gig lgisvt 0.375 0.5 0.15 0.2 urea beads--. do clear, good color 81,000 75 10 B-nied: v1s# 1.5 2.0 0.15 0.2 0.02 0.027 do powder -110 clear, 51. discol- 73,000

. ore

75 10 do 1.5 2.0 0.15 0.2 0.02 0.027 thiourea beads..." discoloredclear, discolored- 74,500

1 A. S. T. M. Heat of Distortion: 94 0.; also heated only 8 hrs. instead of 24 hrs.

1.5 parts of polyvinyl alcohol (type B, medium viscosity, #349) 0.02 part of potassium pers-ulfate (0.1% aqueous solution) 0.15 part of benzoyl peroxide 0.0225 part of melamine 730 parts of distilled water The polyvinyl alcohol is dissolved in the water by stirring at room temperature for about 15 minutes followed by heating on a steam bath. The solution is then filtered and introduced into a vessel equipped with a reflux condenser, a thermometer and agitating means. An atmosphere of carbon dioxide is provided by introduction of the gas through the top of the condenser.

The benzoyl peroxide is dissolved in the styrene at room temperature, the resultin solution is filtered, and the filtered solution is introduced into the vessel containing the solution of polyvinyl alcohol. The melamine and potassium persulfate solution are then added.

The reaction mixture is heated with stirring at 85 C. for 24 hours and then steamed to recover unpolymerized monomer which is less than 1.5 parts. The styrene polymer which is obtained as a finely divided powder of excellent color is refined by collecting on a filter and washing by suspension in 4 volumes of ice water. The temperature of the water is raised to room temperature by allowing the suspension to stand and finally brought up to about 75-80 C. by heating on a steam bath. The polystyrene is filtered, the refining procedure is repeated twice, and the final polymer is then dried at 85-90 C. in a vacuum oven for 48 hours. The extensive refining process is necessary for substantial removal of all occluded polyvinyl alcohol from'the polystyrene.

The polymer obtained by the process described above is calculated to have a Staudinger molecular weight of 68,500, and moldings made therefrom are clear and of good color.

The general procedure of Example 1 is repeated with variations in the type and amount of disparsing agent, the kind and amount of catalyst and the type of modifying nitrogen compound used, other proportions, etc.,-beingkept constant.

If polystyrene is prepared in accordance with the general process of Example 1 but without any nitrogen compound, the polymeric product is normally highly discolored and it has a Staudinger molecular weight of-around 37,000. These control figures will facilitate evaluation of the results listed in Table I.

Thus, it wi11 be apparent that polystyrene of modified physical properties may be obtained according to the process of the present invention using from about 0.02% to 2% total catalyst, based on the weight of monomeric styrene. Using a constant 0.03% or nitrogen-containing compound, also based on the weight of monomeric styrene, theweight ratio of Nitrogen-containing compound Total catalyst ranges correspondingly from 1.5 to 0.015. The type and amount of polyvinyl alcohol emulsifying agent seem to have little effect on the molecular weight of the final polymer.

EXAMPLE 2 parts of ethyl acrylate 25 parts of a 10% aqueous solution of Aquarex D 1 0.025part of potassium persulfate (0.1% aqueous solution) 002. part of meta-aminophenol parts of distilled water The 'm-aminophenol is mixed with the "ethyl acrylate 'andthis"m'i'xture, alongwith the other ingredients listed above, is placed "in a vessel equipped with a reflux condenser and means for agitation. The reaction mixture is heated on a steam batnwithstirrin'g. Polymerization starts in '54; minutes andis complete in about 15 minutes. After 30 minutes, the reaction mixture is steamedtoremove all volatile material and then filtered, "cooled'and 'coag'ulated 'with'methanol. The 'fcoagulated polymer is washed free of the emulsifying agent'an'd dried in 'a'n'airoven at 100C. forl'dhours.

Aquareir -D consists of rue sodium salts of sulfate monoesters of a mixture of higher fatty alcohols chiefiy lauryl and myristyl derivatives, and is neutral in reaction.

be found in Table II. I

Table II Time flow of 17 Staudinger Rela- C-NH: Oomsolution of 0 Molecular ti ve pound polymer in Weight of V1s- 51c toluene Polymer eosity Y m-aminophenol 32 min. 47 sec. l, 180, 000 35. 2 3. 56 m-phenylenedm- 32 min. sec 1, 160,000 34. 7 3. 54

none. melamine 37 min. 11 sec 1, 390, 000 4.14 3. 72 ethyl 1somelamine. 21 min. 43 sec... 772,000 23. 4 3, 53 phenyl isomela- 25 min 694, 000 26.9 3. 29

mine. urea 32 min. 56 sec... 1, 185, 000 35. 4 3. 56 thiourea 42 min. 27 sec 1, 540, 000 45. 7 3. 82 semi-carbaz1de..... 10 min. 34 sec 359, 000 11. 4 2. 43

Nitrogen-containing compound Catalyst for this set of polymerization processes according to the present invention is 0.8 since 0.02% of compound and 0.025% of catalyst, both figures based on the weight of ethyl acrylate, are used in each case. The amount of catalyst may be varied, however, a range of 0.02% to 2% being a practical operating range though by no means the limit.

The modifying effects of the nitrogen compounds in the process of the present invention are only obtainable ii polymerization is carried out in a non-acidic aqueous medium. Thus, the monomeric materials containing a single polymerizable CH2=C group may be polymerized in neutral or alkaline aqueous dispersions or emulsions.

In the former case, suitable dispersing agents which may be used include talc, calcium phos phate, styrene-maleic acid hetercpolymers, dimethyl styrene-maleic methyl cellulose, methyl starch, glycol cellulose, gums, polyacrylamide, etc.

In the latter case it must be borne in mind that since the aqueous medium must be neutral or alkaline, cationic emulsifying agents are unsuitable. Neutral or anionic emulsifiers which may be used include, for example, sodium hydroxystearate, the sodium salts of long-chain sulfated alcohols such as sodium lauryl sulfate, the sodium salts of organic sulfonates including the sodium salts of alkyl substituted naphthalene sulfonic acids, the sodium salts of the alkyl esters of suliosuccinic acid such as the sodium salt of the dioctyl ester of sulfosuccinic acid, etc. Mixtures of the various emulsifying agents may be used if desired.

Monomeric substances containing a single polymerizable CH2=C group which may be polymerized according to the process of the present invention to produce a soluble thermoplastic polymer of modified physical properties include,

acid heteropclymers,

inaddition to the styrene and ethyl acrylate of the specific examples, monoalkyl substituted styrenes such as the ortho, metaand paramethyl styrenes, the ortho-, metaand paraethyl styrenes, the ortho-, meta and para-propyl styrenes, etc. The alkyl substituent may contain, in general, from 1 to 6 carbon atoms. Monohalogenated styrenes such as the ortho, metaand para-chlorostyrenes, the ortho-, metaand para-bromostyrenes, etc., may also be used. Other alkyl esters of acrylic acid having from 1 to 6 carbon atoms in the alkyl group such as methyl acrylate, propyl acrylate, isobutyl acrylate, hexyl acrylate, etc., fall within the scope of the present invention as do the corresponding alkyl esters of methacrylic acid and other alkacrylic acids having from 1 to 6 carbon atoms in the alkyl group of the ester portion of the compound and from 1 to 3 carbon atoms in the alkyl group of the acid portion or the molecule, acrylic acid itself, methacrylic acid and ethacrylic acid, acrylonitrile, acrylamide, methylol acrylamide, methacrylamide, methylol methacrylamide, N-alkyl acrylamides, di-N-alkyl acrylamides, vinyl esters such as vinyl chloride, vinyl acetate, etc. Mixtures containing two, three, eight, eleven or an infinite number of monomeric substances, each containing only a single polymerizable CH2=C group, may be polymerized according to the process of the present invention which is therefore applicable to the improvement of such useful copolymers as those of acrylamide and acrylic acid esters, of acrylonitrile and acrylic acid esters, of styrene and acrylonitrile, of styrene, acrylonitrile and acrylate, etc.

Organic nitrogen compounds containing the group are generally suitable for use as modifying compounds in the process of the present invention. Examples of such organic nitrogen compounds include urea, thiourea, substituted ureas and thioureas such as methylol urea, N-ethyl thiourea, N,N-dimethylurea, etc., guanidine and substituted guanidines such as N-methyland N- phenyland N,N-dibenzyl-guanidines, biguanide and substituted biguanides such as N-alkyl-, Naryl-, N-aralkyland corresponding N,N-disubstituted biguanides, dicyandiamide, aminosubstituted aromatic compounds such as the ortho-, metaand para-aminophenols, the ortho-, metaand para-phenylene diamines, etc., melamine, substituted melamines, isomelamines such as ethyl-isomelamine and phenylisomelamine, etc. It is interesting to note that of the aromatic amino compounds, those possessing a meta substitution are by far the most effective.

The invention is not limited to the use of any particular peroxide catalyst and those which are suitable include inorganic peroxides, such as hydrogen peroxide, alkali metal persulfates, percarbonates, perborates, etc., as potassium persulfate, sodium percarbonate, potassium perborate, etc. These catalysts are water-soluble and may suitably be incorporated in the aqueous phase of the polymerizable emulsion or dispersions. Organic peroxides suitable for use which include benzoyl peroxide, benzoyl acetic peroxide, lauroyr'peroxide, oleic peroxide, stearic peroxide, acetic peroxide, etc., are preferably incorporated in the non-aqueous phase. Mixtures of two or more,

7 up to and including an infinite numberof catalysts maybe used, certain combinations of catalysts favoring particular physical forms of polymers.

Relatively small proportions of polymerization catalysts are used and, in general, from 0.01%% thereof, based on the weight of polymerizable material, is sufficient to increase the rate of polymerization of the monomer and, in conjunction with the proper amounts of nitrogen-containing compound, to produce a desired property modi fication in accordance-ith the present invention. I prefer limiting the amount of catalyst to from 0.02%-2% in usual 'cases'.

The particular amount of nitrogencompound used according to the process of the present in vention is largely dependent upon the amount of peroxide catalyst present and upon the nature of the monomeric substance to be polymerized. In the polymerization of ethyl acrylate, for example, an ideal combination consists of about 0.025% catalyst and 0.02% nitrogen compound in which case the ratio of nitrogen compound to catalyst is 08. Excellent results can be obtained in the polymerization of styrene if from 0.02% to 2% catalyst and 0.03% nitrogen compound are used, theratio of nitrogen compound to catalyst rang ing from 1.5 to 0.015. Generally, it will be undesirable from a practical standpoint to use more \C=NH2 compound than catalyst and accordingly the ratio of nitrogen compound to catalyst is preferably maintained between about 0.01 and 1.0 regardless of the particular monomeric compound, and this range constitutes the preferred embodiment of my invention.

The thermoplastic polymers prepared according to the process of the present invention are soluble in organic solvents and possess unique properties, largely occasioned by the increased molecular Weights, which render them admirably suited for many applications.

The time of flow of a 1% solution in toluene of the polymers of the specific examples is determined by dissolving 1 gram of the dry polymer in 100 cc. of toluene at 25 C. cc. of this solution are then placed in a viscosimeter tube #100 and its time of flow determined at 25 C.

From the time flow figure, the relative viscosity may be obtained. It is equal to From the relative viscosity-the intrinsic -viscos* ity which is equal to where m is the relative viscosity and c is the concentration in grams per" cc. of solvent may be calculated.

The Staudinger molecularweight is calculated in the usua1=manner, making use of the equation:

where s' is the specific visco'sity,c istheconcen- .tratio n, Km i a characteristic constant and M .is the molecular weight.

I claim:

A process for modifying the physical properties of a homopolymer of ethyl acrylate which consists in polymerizing monomeric ethyl acrylate in a non-acidic aqueous medium in the presence of 0.02% by weight of 'm-phenylenediamine as the solemodifying agent and 0.025% by weight of a peroxide polymerization catalyst, whereby'a homopolymer of ethyl acrylate of greatly increased molecular Weight is obtained.

EDWARD L. KROPA.

REFERENCES CITED The following references are of record in the file of this-patent:

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